The inventions described below apply generally to wastewater treatment processes and systems that employ activated sludge. More specifically, the inventions are directed to the enhanced removal of suspended solids from a fluid stream occasioned by the application of a form of activated sludge during the treatment process.
Typical municipal and industrial wastewater streams contain solid particles in a range of sizes and densities. During conventional treatment processes, solids of larger sizes and densities are removed from the waste stream rather easily. Often, as a primary treatment step, the wastewater is detained in a basin where the heavier particles (those having a density greater than the fluid medium carrying them) settle out of the waste stream through the effects of gravity. Smaller and lighter solids, however, remain suspended in the waste stream requiring additional physical and chemical processing for removal.
Following primary treatment, many treatment processes introduce activated sludge into the waste stream for secondary treatment including additional solids removal. As it is well known in the art, activated sludge is a natural beneficial biomass that interacts with the remaining solids in a manner that creates heavier settleable solids that are then more amenable to physical removal. Some suspended solids remain after the secondary treatment phase leaving a wastewater that it often still unsuitable for discharge or reuse.
Subsequent tertiary treatment processes such as filtration will remove additional solids, but removal is limited by the size of the openings in the filter media. To remove particles that would otherwise pass through the filtration process, conventional wastewater treatment methods call for the introduction of chemical coagulants (such as alum, ferric chloride or organic polymers) prior to filtration. Chemical coagulants interact with suspended solids binding individual particles into larger and heavier solids which can then be removed during secondary treatment.
Wastewater treatment plant operators pay a price for this chemical conditioning. The complex polymer chemicals add significantly to the cost of treatment. Additionally, the chemical sludge that is then collected on the filter can quickly clog or xe2x80x9cblindxe2x80x9d the filter media, requiring frequent, possibly continuous backwashing. This can occur because the combination of the coagulants with the wastewater constituents can create a viscous mat on the filter media. Excessive backwashing reduces the quantity of wastewater that can be treated resulting in either the purchase and installation of more treatment equipment or a reduction in the processes that produce the wastewater. Additionally, the solids removed from the system following chemical addition create a chemical sludge that is more expensive and more difficult to dispose of.
Therefore a method and apparatus for removing suspended solids from a waste stream that reduces or eliminates the need for chemical conditioning is desirable, as well a method and apparatus that is effective at small particle removal that reduces the effect of blinding filter systems and produces a solid waste that is easier to dispose than existing chemical sludges.
The inventions described below reduce or eliminate the need for chemical conditioning of wastewater by reintroducing readily available activated sludge to the treatment process after secondary treatment. An advantage of this method is that activated sludge provides a natural coagulant without the expense of chemical addition as suspended solids are adsorbed onto the activated sludge. The natural waste solids avoid the problems of heavy chemical concentrations and are thus more readily disposable.
Definition of Terms
The following terms are used in the claims of the patent and are intended to have their broadest meaning consistent with the requirements of law:
coagulationxe2x80x94the agglomeration of small, dispersed solids into larger particles more amenable to settling or filtration.
Where alternative meanings are possible, the broadest meaning is intended. All words in the claims are intended to be used in the normal, customary usage of grammar and the English language.